This invention relates to a photo-degradable resin composition which becomes rapidly aged and brittle due to direct irradiation of the sun light or ultra-violet rays, resulting in easy breakage owing to the weathering effect, or even by a slight artificial or mechanical shock from outside.
With increase in consumption of plastic wrapping materials, one-way containers, and so forth, these plastic wastes have brought about serious social problems as one of the undesirable causes of environmental pollution.
One method of solving such problem is to use containers or wrapping materials made of a resin composition having a photo-degrading property which causes the used containers, etc., when they are left outdoors, to be degraded by deterioration and enbrittlement due to the direct sun light, ultra-violet rays, or weathering effect.
The photo-degradable resin composition to be used for this purpose should be one that, when left outdoors, it is prone to be deteriorated or aged by light irradiation, and, at the same time, it still possesses sufficient mechanical strength required of the plastic material during the period of use.
There has been used, for a variety of purposes, the so-called graft copolymer (hereinafter referred to as butadiene type graft copolymer) produced by graft-polymerizing one or more kinds of vinylidene type monomer upon a butadiene polymer rubber or a copolymer of butadiene, as a principal component, and another monomer copolymeriazble therewith, either alone or as a blend with other plastic components.
This type of graft copolymer, or a resin composition containing therein such graft copolymer as the major constituent, for use in manufacturing shaped articles usually contains therein 20% by weight or so of the butadiene component, and the graft copolymer containing therein more than 30% by weight of butadiene has been especially used as an impact modifier to be blended with other plastic components in a major quantity.
In using the butadiene type graft copolymer as the impact modifier, the weather resistance thereof has been the problem, and there has been frequently practised addition of a stabilizer to this graft copolymer to prevent the shaped articles made thereof from becoming aged and brittle. In spite of such fact, however, there has been made not a single proposal to use this butadiene type graft copolymer as a blending component for the photo-degradable resin material.
The present inventors have recognized that a graft copolymer containing therein at least 30% by weight of butadiene, in terms of its monomer unit, which is obtained by graft-polymerizing at least one kind of vinylidene type monomer with a rubber polymer selected from butadiene polymer, or copolymers containing therein butadiene as the principal constituent is particularly remarkable in its aging due to the light irradiation. As the result of further studies and researches on improvement in the photo-degrading property thereof, they have found that the copolymer having a cross-linked graft portion (plastic component) by addition of a small amount of a cross-linking agent at the time of graft-polymerization of the vinylidene type monomer is exceedingly superior in its photo-degrading property as compared with a copolymer having a non-cross-linked graft portion.